The present invention relates to facilities for the automatic assembly of mechanical parts and more particularly to a parts supply system for automatically and continuously supplying a plurality of kinds of parts to a robot installed in such facilities.
A parts supply system for the above application is disclosed in, for example, Japanese Patent Laid-Open Publication No. 1-40236 and capable of automatically supplying parts to a robot at high speed. The conventional parts supply system has a buffer for receiving a stack of trays each storing a particular kind of parts from an unmanned vehicle. A separating mechanism is included in the buffer and separates one of the trays from the overlying and underlying trays and transfers it to an elevator. A stocker has a plurality of stocking positions arranged in the vertical direction and each storing a particular kind of parts. The stocker is movable up and down to supply the parts to a robot. The elevator moves the separated tray to one of the stocking positions of the stocker which should be replenished with parts. The stocker is raised or lowered to replace an empty tray dealt with by the robot with the full tray brought thereto by the stocker. The full tray is pulled out from the stocker to supply parts to the robot. On the other hand, the elevator is further lowered to put the empty tray on the top of a stack of empty trays. These empty trays are collectively transferred from the elevator to the bottom portion of the unmanned vehicle.
The conventional parts supply system described above has the following problems left unsolved.
(1) In the buffer, one tray must be separated from both the overlying trays and the underlying trays. Therefore, it is necessary to memorize all the trays stacked on the buffer, their heights, and the kinds of parts contained in the respective trays, and to compute a height for effecting the separation. This is not practicable without resorting to a control unit having advanced storing and computing functions. In addition, the separating mechanism and control are complicated. Moreover, when the number and the kind of parts to be assembled, particularly the height of a tray, is changed, the control program must be modified at the cost of time, labor and expense.
(2) The stocker must move up and down in order to supply the robot with parts from the trays each containing a particular kind of parts at a predetermined height and to replace the empty and full trays at a predetermined height. In addition, the tray containing a required kind of parts must be pulled out in order to supply them to the robot. As a result, the structure of the stocker and the control are complicated.
(3) In the event of replacement, the empty tray is pulled out of the stocker, and then the full tray is pushed into the stocker. These two movements occur alternately and in the opposite directions to each other. Hence, the replacement consumes a disproportionate time and further complicates the structure and control.
(4) Since the parts supply system is constructed into integral equipment, it cannot readily adapt to a change in the number of parts and must maintain, even when the number of parts is reduced, a condition capable of accommodating the maximum number of parts.
(5) Usually, a manual control function is required which can cause each section of the device to operate independently of the others for adjustment or removal of an error. It has been customary to provide this kind of device with manual control switches for the respective sections. This is problematic since the switches are not needed while the device is normal and, therefore, waste space, time, and cost.